1. Field of the Invention
The present invention is related to a process for the fabrication of a molded part with circular cross section, such as a screw, a nut, a socket, a pipe connector part, a pipe connector or similar, with the molded part designed with a hollowed-out cylindrical base body. The inner channel of the molded part, designed for the sealing reception of a connector part, is equipped with segments with various functions in axial direction for the application of a peripheral gasket, for the direct or indirect mounting, and/or arrest of the connector part, and/or for the support, and/or guiding of the connector part, with the base body featuring at least one internal thread, and/or external thread, where a fiber-containing plasticized polymeric mass is injected into the cavity of a molding tool via at least one injection port of a molding tool. Following the hardening of the polymeric mass, the molded part is removed from the tool. In addition, the present invention relates to a molded part that can be fabricated pursuant to such process.
2. Related Technology
Injection molding is a known, discontinuous forming process, used in particular for plastics. Injection molding allows the large-volume and high-accuracy production of industrial molded parts for immediate use. For that purpose, the respective material, and/or the molding compound, is plasticized in the injection unit of an injection-molding device, and injected into an injection-molding tool. Modern injection molding devices use a worm gear, which plasticizes, transports, and injects the molding compound into the tool. The polymeric mass solidifies inside the cavity and/or mold cavity of the tool. After the solidification, the molded part can be removed from the tool. Generally, the volume loss due to the solidification can be balanced with post-pressure applied prior to the removal—but only to a certain extent. Injection molding may be used for the processing of thermoplastics, thermosetting and elastomeric materials. It is also known technology to use masses containing fibers for the injection molding of thermoplastics, which allows the fabrication of molded parts with comparably higher stability.
A process and a molded part of the type mentioned above are known in WO 2009/124994 A1. A similar molded part is described in DE 10 2010 010 651 A1, with its particular characteristic consisting of the base body of the molded part on one hand, and existing thread gaskets, and/or peripheral gaskets on the other hand, which may be produced from various polymeric materials in a multi-component injection molding process.
Pursuant to the process established in WO 2009/124994 A1, injection into the cavity through a minimum of two injection ports may be carried out in such manner that the fibers will align predominantly in accordance with the maximum shear stress of the molded part, axial tension, and torsion. Injection is carried out in axial direction, with the mass flowing around the internal core of the tool in a circle, converging at the injection ports. Joint lines form at these locations, usually with less stability than the remaining body of the molded part. The structure of the established molded part meeting the operational demands consists on one hand of part of the fibers aligned in circumference-appropriate direction of the circular cross segment at right angles towards the longitudinal axis of the molded part. On the other hand, the structure also consists of one part of the fibers aligned in axial direction of the molded part, each respectively smaller than 50 percent. Surprisingly, this process helps to compensate, at least partly, a negative effect by the joint seam. However, it has been shown that in industrial use, especially with threaded parts, the operational demand of the molded part on the torsion is of less importance than the operational demand of the molded part on the axial tension, with the maximum torque of inserting or unscrewing the molded part without breaking playing a significant role. This results in particular in a demand for increased shear strength, as well as increase in the post-pressure effectiveness. Post-pressure effectiveness means, in particular, that the post-pressure applied leads to homogeneous filling of the cavity, free of hollow spaces, and—if joint seams do exist—to a high degree of joint seam stability. With the described and known multiple gates process a balanced filling of the cavity cannot be guaranteed in every case without additional process-stabilizing measures whenever hot runner nozzles are utilized.